The present invention relates to instruments which operate on the principle of pulse oximetry, in particular, to non-invasive hemoglobin saturation detectors and methods, and may be generally applied to other electro-optical methods of measuring blood constituents.
Electro-optical measurement of blood characteristics has been found to be useful in many areas of blood constituent diagnostics, such as glucose levels, oxygen saturation, hematocrit, billirubin and others. This method is advantageous in that it can be performed in a non-invasive fashion. In particular, much research has been done on oximetry, a way of measuring oxygen saturation in the blood, as an early indicator of respiratory distress.
Infants during the first year of life are susceptible to breathing disturbances (apnea) and respiratory distress. Sudden Infant Death Syndrome (SIDS) is a medical condition in which an infant enters respiratory distress and stops breathing, leading to the death of the infant. Although the cause and warning signs of SIDS are not clear, it has been shown that early detection of respiratory distress can provide the time to administer the aid necessary to prevent death.
Many types of baby monitors are currently available, from simple motion detectors to complicated systems which stream oxygen enriched air into the infant""s environment. Some of the more accepted monitoring methods include chest motion monitors, carbon dioxide level monitors and heart rate (pulse) monitors. Unfortunately these methods often do not give the advance warning necessary for the caregivers to administer aid. In addition, these monitors are administered by attaching a series of straps and cords which are cumbersome to use and present a strangulation risk.
The chest motion monitor gives no warning when the breathing patterns become irregular or when hyperventilation is occurring, since the chest continues to move. Distress is only noted once the chest motion has ceased at which point there may only be a slight chance of resuscitation without brain damage. In addition these devices are known to have a high level of xe2x80x9cfalse alarmsxe2x80x9d as they have no way to distinguish between the lapses in breathing which are normal for an infant (up to 20 seconds) and respiratory distress. These devices can cause excessive anxiety for the caregivers or cause them to ignore a signal which is true after responding repeatedly to false alarms.
Among other symptoms, SIDS causes an irregular heartbeat, resulting eventually in the cessation of heartbeat with the death of the infant. There are some instruments which use the EKG principle to monitor this clinical phenomenon. This is a limited method which has a very high rate of false positives since the monitors have inadequate algorithms to determine what is a SIDS event. Obviously, this is not a convenient method, nor is it desirable to have the infant constantly hooked up to an EKG monitor.
In light of these disadvantages a better method to use is a form of electro-optical measurement, such as pulse oximetry, which is a well-developed art. This method uses the difference in the absorption properties of oxyhemoglobin and deoxyhemoglobin to measure blood oxygen saturation in arterial blood. The oximeter passes light, usually red and infrared, through the body tissue and uses a photodetector to sense the absorption of light by the tissue. By measuring oxygen levels in the blood, one is able to detect respiratory distress at its onset giving sufficiently early warning to allow aid to be administered as necessary.
Two types of pulse oximetry are known. Until now, the more commonly used type has been transmission oximetry in which two or more wavelengths of light are transmitted through the tissue at a point where blood perfuses the tissue (i.e. a finger or earlobe) and a photodetector senses the absorption of light from the other side of the appendage. The light sources and sensors are mounted in a clip which attaches to the appendage and delivers data by cable to a processor. These clips are uncomfortable to wear for extended periods of time, as they must be tight enough to exclude external light sources. Additionally, the tightness of the clips can cause hematomas. Use of these clips is limited to the extremities where the geometry of the appendages is such that they can accommodate a clip of this type. The clip must be designed specifically for one appendage and cannot be used on a different one. Children are too active to wear these clips and consequently the accuracy of the reading suffers.
In another form of transmission oximetry, the light source and detector are placed on a ribbon, often made of rubber, which is wrapped around the appendage so that the source is on one side and the detector is on the other. This is commonly used with children. In this method error is high because movement can cause the detector to become misaligned with the light source.
It would be preferable to be able to use the other type of pulse oximetry known as reflective, or backscattering, oximetry, in which the light sources and light detector are placed side by side on the same tissue surface. When the light sources and detector can be placed on the tissue surface without necessitating a clip they can be applied to large surfaces such as the head, wrist or foot. In cases such as shock, when the blood is centralized away from the limbs, this is the way meaningful results can be obtained.
One difficulty in reflective oximetry is in adjusting the separation between the light source and the detector such that the desired variable signal component (AC) received is strong, since it is in the alternating current that information is received. The challenge is to separate the shunted, or coupled, signal which is the direct current (DC) signal component representing infiltration of external light from the AC signal bearing the desired information. This DC signal does not provide powerful information. If the DC signal component is not separated completely, when the AC signal is amplified any remaining DC component will be amplified with it, corrupting the results. Separating out the signal components is not a simple matter since the AC signal component is only 0.1% to 1% of the total reflected light received by the detector. Many complicated solutions to this problem have been proposed.
If the light source and detector are moved further apart, this reduces the shunting problem (DC), however, it also weakens the already weak AC signal component. If the light source and detector are moved close together to increase the signal, the shunting (DC) will overpower the desired signal (AC).
Takatani et al., in U.S. Pat. No. 4,867,557, Hirao et al., in U.S. Pat. No. 5,057,695 and Mannheimer, in U.S. Pat. No. 5,524,617 all disclose reflective oximeters which require multiple emitters or detectors in order to better calculate the signal.
A number of attempts have been made to filter out the DC electronically (see Mendelson et al., in U.S. Pat. No. 5,277,181). These methods are very sensitive to changes in signal level. The AC remaining after the filtering often contains a small portion of DC, which upon amplification of the AC becomes amplified as well, resulting in inaccurate readings. Therefore, this method is only useful in cases where the signal is strong and uniform.
Israeli patents 114082 and 114080 disclose a sensor designed to overcome the shunting problem by using optical fibers to filter out the undesired light. This is a complicated and expensive solution to the problem which requires a high level of technical skill to produce. In addition, it is ineffectual when the AC signal is relatively weak.
As can be seen from the above discussion, the prior art methods of addressing the AC/DC signal separation problem in reflective oximetry techniques are complicated and expensive. Therefore, it would be desirable to provide a simple, low cost and effective method for achieving accurate reflective or transmissive oximetry detection of respiratory stress.
Accordingly, it is the broad object of the present invention to overcome the problems of separating the shunted light from the signal in order to provide a physiological stress detector which achieves accurate readings.
A general object of this invention is to overcome the problems of separating the shunted light from the signal in order to provide a respiratory stress detector which achieves accurate pulse oximetry readings for respiratory stress applications.
The present invention discloses a small, independent, sensor, for invasive and non-invasive applications unencumbered by cables or wires, which is capable of being attached to different body parts, to comfortably and accurately monitor blood constituent levels and the pulse of an infant or any other living organism. The apparatus may be applied to any part of the body without prior calibration. Accurate readings of blood constituent levels are obtained using the inventive method in which a precise separation of the AC and DC signal components has been achieved, allowing each signal component to be amplified separately. In order to accomplish this precise separation, the signal components are separated by a novel signal processing technique.
The inventive sensor may be adapted for many health monitoring situations including infant monitoring for SIDS, fetal monitoring, etc.
In a preferred embodiment adapted for SIDS, the sensor is designed to apply reflective oximetry techniques, so as to comfortably and accurately monitor the arterial oxygen levels and the pulse of an infant or any other living organism prone to respiratory distress. This monitor is equipped with a processor capable of determining the need for an alarm and capable of signalling a distress signal to further alert to a crisis.
In another embodiment, in addition to the alarm being generated from the sensor itself, readings will be radio-transmitted to a base station, possibly at a nurse""s station, to allow monitoring of the reading, and another alarm will be activated from the base station when the readings are outside of the accepted range.
In another preferred embodiment, the apparatus is mounted in a sock-type mounting such that the apparatus is properly applied when the sock is put on in the usual fashion. In addition, the sock-type apparatus blocks entrance of external light to the area of the sensor apparatus.
In yet another preferred embodiment, the apparatus is mounted on a ribbon-type mounting such that the apparatus is properly applied when the ribbon is tied around the head or other body part. In addition, the width of the ribbon is such that it will block entrance of external light to the area of the sensor apparatus. Additionally, the ribbon may be of dark color which also blocks entrance of external light to the area of the sensor apparatus.
In yet another preferred embodiment, the apparatus is mounted on a bracelet-type mounting such that the apparatus is properly applied when the bracelet is fastened to the wrist or other body part. In addition, the width of the bracelet is such that it blocks entrance of external light to the area of the sensor apparatus. Additionally, the bracelet may be of dark color which also blocks entrance of external light to the area of the sensor apparatus.
There is therefore provided, in accordance with a preferred embodiment of the present invention, A non-invasive device disposed proximate the surface of an organ for measurement of a level of at least one blood constituent. The device includes: at least one light source, providing light directed toward the surface of the organ, the light being reflected from the organ, a light detector spaced apart from the at least one light source and being sensitive to intensity levels of the reflected light for producing intensity signals in accordance therewith, and a processing unit for processing the intensity signals received from the light detector. The processing unit includes: first and second amplifiers for amplifying the intensity signals, each in accordance with a respective first and second gain amplification factor, and a processor for automatically determining the first and second gain amplification factors in adjustable fashion. During a first stage, the first and second amplifiers amplify a DC signal component of the intensity signals in accordance with predetermined first and second gain amplification factors, the DC signal component is subtracted from the intensity signals at an input of the first amplifier, to isolate an AC signal component of the intensity signals. During a second stage, the second amplifier amplifies the isolated AC signal component in accordance with the adjustably-determined second gain amplification factor. The processing unit produces output signals in accordance with the isolated AC signal component and the DC signal component and calculates in accordance therewith, at least one blood constituent level.
Furthermore, in accordance with another preferred embodiment of the present invention, the light source and the light detector of the device are held in a spaced relationship while in contact with the surface of the organ so as to substantially block entrance of external light therebetween.
Furthermore, in accordance with another preferred embodiment of the present invention, the processing unit further comprises: means for normalizing the AC and DC output signal components to produce first and second normalized signals, and means for forming a ratio of the first and second normalized signals. The processor calculates the blood constituent level in accordance with the ratio.
Furthermore, in accordance with another preferred embodiment of the present invention, the organ is the skin and the device is arranged for mounting on a ribbon, a bracelet and the like for placement on a part of a human or an animal body.
Furthermore, in accordance with another preferred embodiment of the present invention, the organ is the skin and the device is arranged for mounting on a tightly-fitted garment to be worn over a part of the body.
Furthermore, in accordance with another preferred embodiment of the present invention, the device further includes a transmitter for transmitting the output signals to a receiver at a remote location, allowing monitoring of the at least one blood constituent level from the remote location. The receiver is equipped with an alarm unit for alerting when the at least one blood constituent level falls outside of a predetermined range.
Furthermore, in accordance with another preferred embodiment of the present invention, the processor develops a control signal when the adjustably-determined second gain amplification factor is established in the second stage, the signal is measured and the control signal shuts off the light source.
Furthermore, in accordance with another preferred embodiment of the present invention, the control signal conserves energy by reducing the operational duty cycle of the light source.
Furthermore, in accordance with another preferred embodiment of the present invention, the first and second gain amplification factors are determined by the processor in an iterative process by adjustably setting a gain amplification factor and measuring a dynamic voltage range of the output signals to determine if the voltage range falls within a predetermined window established by the processor.
Furthermore, in accordance with another preferred embodiment of the present invention, the light source comprises a single light emitting unit capable of controllably providing light having a wavelength range selected from at least a first wavelength range and a second wavelength range. The first wavelength range is at least partially different from the second wavelength range. The single light emitting unit can be switched from emitting light within the first wavelength range to emitting light within the second wavelength range.
Furthermore, in accordance with another preferred embodiment of the present invention, the light source includes at least a first light emitting unit capable of controllably emitting light having a first wavelength range and a second light emitting unit capable of controllably emitting light having a second wavelength range. The first wavelength range is at least partially different from the second wavelength range.
Furthermore, in accordance with another preferred embodiment of the present invention, the light source provides light having wavelengths in the red and infrared ranges.
Furthermore, in accordance with another preferred embodiment of the present invention, the organ is the skin, the blood constituent is hemoglobin, and measurement of a level of oxygen saturation in the hemoglobin provides an early indication of respiratory stress.
Furthermore, in accordance with another preferred embodiment of the present invention, the respiratory stress is associated with Sudden Infant Death Syndrome.
Furthermore, in accordance with another preferred embodiment of the present invention, the device produces an output signal sent by the processor to an alarm unit for alerting when the at least one blood constituent level falls outside of a predetermined range.
Furthermore, in accordance with another preferred embodiment of the present invention, the device is used to monitor the heart rate.
Furthermore, in accordance with another preferred embodiment of the present invention, the device is used as an apnea monitor.
Furthermore, in accordance with another preferred embodiment of the present invention, the device is a portable hand held reflective pulse oximeter.
Furthermore, in accordance with another preferred embodiment of the present invention, the device is adapted to determine blood billirubin levels.
Furthermore, in accordance with another preferred embodiment of the present invention, the device is adapted for mapping the intensity of the AC signal along the surface of the organ to detect regions of the organ having a reduced blood flow.
There is further provided, in accordance with another preferred embodiment of the present invention, a method for non-invasive measurement of a level of at least one blood constituent. The method includes the steps of: providing light from at least one light source disposed proximate the skin, directing the light toward the skin surface, the light being reflected from the skin, providing a light detector spaced apart from the light source and being sensitive to intensity levels of the light reflected from the skin for producing intensity signals in accordance therewith, and processing the intensity signals received from the light detector. The processing step includes the steps of amplifying the intensity signals in first and second amplifiers, each in accordance with a respective first and second gain amplification factor, and automatically determining the first and second gain amplification factors in adjustable fashion. During a first stage, the first and second amplifier amplify a DC signal component of the intensity signals in accordance with predetermined first and second gain amplification factors, the DC signal component being subtracted from the intensity signals at an input of the first amplifier, thereby isolating an AC signal component of the intensity signals. During a second stage, the second amplifier amplifies the isolated AC signal component in accordance with the adjustably-determined second gain amplification factor. The processing step produces output signals in accordance with the isolated AC signal component and the DC signal component and calculates in accordance therewith, the at least one blood constituent level.
Furthermore, in accordance with another preferred embodiment of the present invention, the method further includes the step of transmitting the output signals to a receiver at a remote location, allowing monitoring of the at least one blood constituent level from the remote location. The receiver is equipped with an alarm unit for alerting when the at least one blood constituent level falls outside of a predetermined range.
Furthermore, in accordance with another preferred embodiment of the present invention, the step of processing further includes normalizing the AC and DC output signal components to produce first and second normalized signals, forming a ratio of the first and second normalized signals, and calculating the blood constituent level in accordance with the ratio.
Furthermore, in accordance with another preferred embodiment of the present invention, the method further includes the steps of developing a control signal when the adjustably-determined second gain amplification factor is established in the second stage, measuring the signal and shutting off the light source in response to the control signal.
Furthermore, in accordance with another preferred embodiment of the present invention, the method further includes the steps of determining the first and second gain amplification factors by a processor in an iterative process by adjustably setting a gain amplification factor, and measuring a dynamic voltage range of the output signals to determine if the voltage range falls within a predetermined window established by the processor.
Furthermore, in accordance with another preferred embodiment of the present invention, the blood constituent is hemoglobin, the method further includes the step of measuring a level of oxygen saturation in the hemoglobin providing an early indication of respiratory stress.
Furthermore, in accordance with another preferred embodiment of the present invention, the respiratory stress is associated with Sudden Infant Death Syndrome.
Furthermore, in accordance with another preferred embodiment of the present invention, the method further includes the step of initiating an alarm for alerting when the blood constituent level falls outside of a predetermined range.
Furthermore, in accordance with another preferred embodiment of the present invention, the alarm is selected from an audible alarm, a visual alarm, a tactile alarm, dialing a telephone number and any combination thereof.
Furthermore, in accordance with another preferred embodiment of the present invention, the light is alternatingly selected from at least a first wavelength range and a second wavelength range. The first wavelength range is at least partially different from the second wavelength range.
Furthermore, in accordance with another preferred embodiment of the present invention, the first wavelength range includes wavelength of red light and the second wavelength range includes wavelength of infra-red light, the blood constituent is hemoglobin and the method determines the level of oxygen saturation of the hemoglobin.
Furthermore, in accordance with another preferred embodiment of the present invention, the method is used for monitoring the heart rate.
Furthermore, in accordance with another preferred embodiment of the present invention, the method is used for monitoring a condition of apnea.
Furthermore, in accordance with another preferred embodiment of the present invention, the method is used for monitoring the level of billirubin in blood.
Furthermore, in accordance with another preferred embodiment of the present invention. The method further includes the step of repeating the steps of providing light, providing a light detector and processing at a plurality of positions along the skin for mapping the levels of the AC signal component along the surface of the skin to detect regions of reduced blood flow.
There is still further provided, in accordance with another preferred embodiment of the present invention, a method for measurement of a level of at least one blood constituent. The method includes the steps of providing light from at least one light source disposed proximate the surface of an organ, directing the light toward the surface of the organ, the light being reflected from the organ, providing a light detector spaced apart from the light source. The light detector is sensitive to intensity levels of the light reflected from the organ for producing intensity signals in accordance therewith, and processing the intensity signals received from the light detector. The processing step includes the steps of amplifying the intensity signals in first and second amplifiers, each in accordance with a respective first and second gain amplification factor, and automatically determining the first and second gain amplification factors in adjustable fashion. During a first stage, the first and second amplifier amplify a DC signal component of the intensity signals in accordance with predetermined first and second gain amplification factors, the DC signal component is subtracted from the intensity signals at an input of the first amplifier, thereby isolating an AC signal component of the intensity signals. During a second stage, the second amplifier amplifies the isolated AC signal component in accordance with the adjustably-determined second gain amplification factor. The processing step produces output signals in accordance with the isolated AC signal component and the DC signal component, and calculating in accordance therewith, the blood constituent level.
Furthermore, in accordance with another preferred embodiment of the present invention, the organ is an internal organ and the method further includes the step of repeating the steps of providing light, providing a light detector, and processing, at a plurality of positions along the surface of the internal organ for mapping the levels of the AC signal component along the surface of the internal organ to detect regions of reduced blood flow.
There is also provided, in accordance with another preferred embodiment of the present invention, a method for non-invasively determining the blood flow velocity in a region of an organ. The method includes the steps of positioning a first pulse-oximetry device and a second pulse-oximetry device proximate the surface of the region. The first and the second device are separated from each other by a predetermined distance, simultaneously obtaining a first and a second sets of data representing the pulsatile variation at the locations of the first and the second device, respectively, as a function of time, each of the first set and the second set of data includes at least one extremum data value, the extremum data value of the first set of data corresponds to the extremum data value of the second set of data, calculating the time interval between the extremum data value of the first set of data and the extremum data value of the second set of data, dividing the value of the predetermined distance by the value of the time interval to obtain a value representing the approximate blood flow velocity in the region of the organ, wherein each of the first device and the second device includes at least one light source, providing light directed toward the surface of the organ, the light being reflected from the organ, a light detector spaced apart from the at least one light source and being sensitive to intensity levels of the reflected light for producing intensity signals in accordance therewith, and a processing unit for processing the intensity signals received from the light detector. The processing unit includes first and second amplifiers for amplifying the intensity signals, each in accordance with a respective first and second gain amplification factor, and a processor for automatically determining the first and second gain amplification factors in adjustable fashion. During a first stage, the first and second amplifiers amplify a DC signal component of the intensity signals in accordance with predetermined first and second gain amplification factors, the amplified DC signal component being subtracted from the intensity signals at an input of the first amplifier, to isolate an AC signal component of the intensity signals. During a second stage, the second amplifier amplifies the isolated AC signal component in accordance with the adjustably-determined second gain amplification factor. The processing unit produces output signals in accordance with the isolated AC signal component and the DC signal component and calculates in accordance therewith.
Furthermore, in accordance with another preferred embodiment of the present invention, the organ is the skin.
Finally, in accordance with another preferred embodiment of the present invention, the extremum data value is selected from a minimum data value and a maximum data value.
Other features and advantages of he invention will become apparent from the following drawings and description.